GENERAL INTRODUCTION TO HEALTH MEASUREMENT (Note: I have added explanatory notes to many of the slides; to see these you will need to save the file and open in the ‘normal view’ mode)

Defining ‘Measurement’ “Measurement consists of rules for assigning numbers to observable attributes so as to represent quantities of the attributes” Lots of words… Let’s try to sort that out… 1. The “attributes” can refer to dimensions, properties, characteristics, or behaviors (e.g., size, density, cost, physical function) 2. If it’s not observable, it’s not measurable (but for health, let’s define observable broadly: if they say they feel bad, you ‘observed’ it). 3. “Operational definitions” indicate how to measure an attribute that is not directly observable (e.g., health, quality of care)

Types of numerical scales Scale Type ExampleUses NominalSex; blood type You can count these (how many females?) Ordinal House numbers; “mild pain” You can compare these ( apply) Interval°C; July 29, 2013 You can calculate absolute differences by adding & subtracting Ratio Weight; BP; # doctor visits You can calculate relative differences: X and ÷ apply Discrete vs. continuous variables; Classifying vs. measuring Mnemonic: NOIR

Measuring vs. Classifying MeasuringClassifying Scientific traditionQuantitativeQualitative studies PurposeCounting, analyzingDescribing; diagnosing DisciplinesSciencesArts; policy Numerical scales Ordinal, interval, ratio scales Nominal, categorical ConceptStateTrait? ApplicationTheoryPractice PhilosophyNomotheticIdiographic Medical examplesEvaluationDiagnosis EffectDividing, splittingGrouping, lumping EssenceBeing?Becoming?

Categories of Health Measures 1. First option: Measures can be classified by their purpose. For example: Evaluative (e.g., clinical trial outcome measures) Diagnostic (e.g., BP, ESR) Prognostic (Apgar; screening tests) Discriminative (e.g., IQ tests; university entrance exams) Summary population measures (e.g., death rates)

6 Purposes for measuring health Describe: Evaluate: Predict: Individual level Population level Clinical History: Signs & symptoms for diagnosis Progress following therapy: before-after comparison To screen for disease (earlier diagnosis) Survey of needs for services e.g. prevalence of disability To evaluate care system: reductions in incidence Planning: projections of future needs for care To

Categories (2) 2. Or, measures may be classified descriptively: Scope of the measure (e.g., specific or generic) Qualitative vs. quantitative (some discussion needed here!) 3. Or methodologically: Subjective vs. objective (how is the information collected?) How it is administered (questionnaires; clinician ratings; laboratory tests) Structured vs. semi-structured How it is scored: indexes vs. profiles

A descriptive range of health indicators Mortality rates (=incidence) Factual, objective Subjective, self-reported Life expectancy Individual level Population level Vital status Disability & handicap surveys; population figures Disability-adjusted life expectancy: DALE, DALYs PYLL: Years of potential life lost Quality-adjusted life years Hospital data: incidence of complications, etc. Impairment Disability Handicap Quality of life (laboratory measures) (clinical assessment) (patient interview)

Health is abstract, so no single indicator. Methodological options: Ask or observe the patientMechanical measures SubjectiveObjective & precise Broad coverage; less specific Focused: cover pieces of the person Communicates the patient’s concerns (illness) What the doctor is interested in (disease) e.g., health measurement scales: Disability; Quality of life; Anxiety or depression; Pain E.g., cultures; chemistry; physiological measures; physical (range of motion, etc)

Choosing & Applying Measurements Choosing Your purpose drives your choice. What type: Specific or generic? Objective or subjective? There are criteria for evaluating & comparing tests Off the peg, or design your own? Where do you get information on a scale? Applying Measures Practical issues: Interview or self- administered? Cost & difficulty How to score it? Analyzing scores Interpreting scores

Choosing a Measurement: How much effort for the respondent? IQ tests, etc. HRQOL. ADLs. EKGs Minimal effort Very demanding: lower response rate?

Match the Instrument to the Application Population Monitoring Outcomes Research Patient Management Source: John Ware, October 2000

Practical issue: Long vs. short versions Measure too low (“ceiling effect”) but retains good discrimination Broad spectrum, but coarse discrimination: may not show changes (broad range + fine discrimination: band width and fidelity) (Source: John Ware, October 2000) The ideal scale Short Forms (same number of items)

Old ways of administering health questionnaires may not be practical Face-to-face Interview$150 + Telephone Interview $ 50 + Self-administered postal$ 20 + Computerized via Web$ <5? (US $)

How to Present Scores? The raw scores Single index value, or a profile of scores Norm-referenced: Z-scores (or other types of standard scores) Percentiles Criterion-referenced: Pass/fail Clinical diagnosis, e.g. based on diagnostic criteria

What’s an “Index”? “Standard, weighted, composite set of indicators” ‘Weighted’ means that each element can receive a different salience in the overall score ‘Composite’ means there’s some way to combine the elements Gives a broad-spectrum indication of overall level of a complex attribute Generally used for broad comparisons Examples: consumer price index; hospital activityindex; Health Utilities Index

Index vs. Profile Cost of living index; Consumer price index Gross national income Physical health Mental Emotional well-being Spiritual Mary Angela EuroQol EQ-5D health index

Raw Scores E.g. on a scale, such as 3MS scores Population distribution can be messy… (Note: we tend to assume, but don’t really know, that the scale points are evenly spaced, as drawn) Maybe the scale spacing should be presented like this, to “bell curve” it?